Optics applets/animation

Refraction, in general:

http://www.absorblearning.com/media/item.action?quick=15n

https://phet.colorado.edu/en/simulation/bending-light

http://www.physicsclassroom.com/Physics-Interactives/Refraction-and-Lenses/Refraction/Refraction-Interactive

And for lenses:

https://phet.colorado.edu/en/simulation/geometric-optics

http://courses.cs.washington.edu/courses/cse131/12au/applets/thinlens.html

Recall also what happens when light hits mirrors (flat and curved).